101413081 surge arrester presentation
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These were previously called Lightning arresters,which is not the correct name or definition.
Surge arrester is a device which protects the electricalexpensive items from damage; like Transformers orReactors or other insulators.
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Expulsion Type.
Gap Type.
Metal oxide Type
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These are also called Non linear resistance typearresters.
Normally Aluminum oxide is used for Metal oxide
because it is cheap and have good characteristics.Due to non linear voltage / current characteristicsit offers low resistance path to the flow of highdischarge current thus limiting the voltage acrossthe arrester terminals.
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It is the maximum permissible voltage which thearrester can withstand, without discharge and without
changing its operating characteristics.
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The voltage which appears across the terminal ofarrester during discharge. The minimum, the better.
The following types of residual voltages are ofimportance.
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Switching impulse residual voltage
It is equipment insulation withstand test voltage with a
front time larger than 30 s.
Lightning impulse residual voltage
It is 1.2/50 s wave shape.
BS use current wave of form 8/20 s for residual voltage.
The above are referred to Arrester Currents.
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TheArrester must be selected with a rated voltagehigh enough towithstand temporary over voltageswhich may be produced by various occurances. Line tofault current is the most common occurance
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There should be sufficient margin between variousrequired impulse and Power frequency withstandvoltages and arrester voltage. It is margin in % and
expressed as:(Insulation withstand voltage Residual voltage) x 100
Residual voltage
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It is the capability of arrester to dissipate a givenamount of energy without damage.
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The ability of arrester to conduct short circuit current
without violent disintegration in the event of itsfailure.
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1. Highest system voltage is the base for Designparameters. It is defined by IEC and otherStandards
2. Temporary over voltages in the system arenormally determined by single line to groundfault.
As such Rated voltage will be differentdepending on the grounding conditionand protection scheme. In case of directlygrounded system the voltage of healthyphase may rise 1.4 times phase to earth voltage.
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where 1.4 is the Earth factor.
3. In case of ungrounded system Earth factor will
be 1.73. Thus the voltage may rise upto 1.73 timesthe phase to Earth voltage.
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3. Check for the abnormal operating conditions,Um.
4. Determine continuous operating voltage (COV)
COV =Um/35. Determine Preliminary rated voltage VR0 based
on COV
6. VR0 = COV/K0 where K0 is Design factor
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6. Determine Temporary over voltage at Earth faultTOVE = KE x COV
7. Select Preliminary Rated Voltage RE based onTOV
E
Determine Rated voltage, RE = TOVE / KT ,where KT isarrester TOV capability expressed as multiple of rated
voltage.
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The following Tests are made on Arresters
Routine Tests1. Power Frequency voltage spark over test on
complete arrester2. Lightning voltage impulse spark over test on
complete arresterVisual examination
3. Residual voltage Test (if agreed between Client andmanufacturer)
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1. Power Frequency Voltage spark over voltage
2. Lightning voltage impulse spark over voltage
3. Switching voltage impulse spark over voltage
4. Spark over voltage/Time curve test5. Residual voltage test
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6. Operating duty
7. Pressure relief test
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System Voltage
Nom./Highest
Arrester Rated
Voltage
Max.Contin-uous
Operating
voltage.
Virtual
Steepness of
Front for Front of
wave
Max. Front of
wave S.O.V
Max. Residual
Voltage
KV KV KV KV (Peak) KV (Peak) KV (Peak)11/12 12 10 100 50 43
66 /72.5 60 46 500 250 216
132/145 120 92 930 463 400
220/245 198 156 1200 746 649
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System Voltage
Nom./Highest
Arrester Rated
Voltage
Max.Contin-uous
Operating
voltage.
Steep current (at
10 KA) 1/20 s
impulse residual
voltage
Lightrning current
(at 10 KA) 8/20
impulse residual
voltage
Switching current
(at 0.5/1KA)
30/60 residual
voltage
KV KV KV KV (Peak) KV (Peak) KV (Peak)
11/12 12 10 40 38 27
66 /72.5 60 46 175 160 130
132/145 120 92 330 295 250
220/245 198 156 545 485 410
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Normal System
Voltage132 KV
Max. system
Voltage, Vmax ==1.1* Vnom KV
= 145 KV
Continuous
operating voltage,
C.O.V
145/1.732 = 84 KV
Earth Factor, KE =1.4
T.O.V == KE * COV
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Assume a working on 132 KV protected by a Surge arrester 25 Meters from Transformer.
Assume velocity, V = 300 m / s
Steepness of Incoming wave =1000 KV/s
Residual voltage, U1 = 276 KV
Voltage Stress, V2 = =276+2*1000*25/300 KV
= 443 KV
BIL of 132 KV System = 650 KV
Margin= =(650-443)/443*100
=47 %